Absorption Frequency Research Articles

Latest Patents on Buffers

Background: When any equipment is running, the physical collision occurs in the machinery, which requires the hydraulic buffer devices to absorb and dissipate the impact energy in order to avoid the large vibration and even the damage to the structure caused by the impact load on the equipment. Therefore, the design of hydraulic buffers is very necessary. Objective: Through the analysis of the research status of hydraulic buffers, some valuable conclusions are extracted from the representative and prospective results to predict the future research and development direction of hydraulic buffers. Methods: The researches on hydraulic buffers are summarized and compared, and the characteristics of energy absorption and energy consumption of hydraulic buffers are expounded. Combined with the principle of hydraulic buffers, the related patents of hydraulic buffer are studied. Results: By tracing the characteristics of different types of hydraulic buffers, the main problems existing in the development of hydraulic buffers are analyzed, such as short working life, low energy absorption efficiency, etc. Solving such problems as a prerequisite, the patents’ development of the structure and design method of hydraulic buffers is prospected. Conclusion: The optimization and development of hydraulic buffers are conducive to improving the energy absorption efficiency and frequency of hydraulic buffers. This paper, thus, summarizes the advantages and disadvantages of different kinds of hydraulic buffers by tracing and summarizing the previous patents, learning that the most widely used buffer is the porous hydraulic buffer, but the cushioning performance of core rod buffer is more, which is the main development trend in the future.

A polarization insensitive terahertz tri-band graphene metasurface absorber

A graphene-based tri-band perfect metasurface absorber is presented for the far-infrared frequency range. A two-dimensional periodic pattern of graphene patches is created on a thin SiO2 dielectric layer, which is backed by a gold ground plane of sufficient thickness ( t ) ensuring zero transmission of the impinging electromagnetic (EM) wave. An array of graphene elliptical discs is placed around graphene square patches and thin graphene strips are used to connect these elliptical patches to the square patches. In terms of the lowest frequency of absorption, the proposed absorber seems to be a thin one as t∼λmax/13. It is also considered compact because the periodicity of the cells is on the order of λmax/22. The absorption spectrum gives three perfect absorption peaks with absorptivity greater than 99% at 5.76 and 9.06 THz. Further, the absorptivity is better than 96% at 7.86 THz. The performance of the proposed absorber remains invariant with change in polarization of the incident wave. It is revealed that this absorber performs satisfactorily throughout a broad angular range of incidence of about ± 60°.

Polarization-insensitive, frequency- and amplitude-tunable transparent microwave absorber based on graphene metasurface

Transparent and flexible metamaterial absorbers can provide solutions for electromagnetic compatibility and electromagnetic radiation pollution. They also play key roles in platforms with optical windows that require low detectability and immunity to electromagnetic interference. Due to the lack of active adaptability to complex electromagnetic environments, early metamaterial absorbers need to be redesigned and manufactured once the application scenarios change. The new two-dimensional material graphene provides a practical technical approach for the realization of transparent tunable absorbers. In this work, we propose a polarization-insensitive dual-tunable microwave absorber based on graphene metasurface. By controlling two separate bias voltages applied to patterned graphene or continuous graphene, independent dynamic regulation of electromagnetic wave absorption frequency and amplitude is achieved. It also possesses the features of optical transparency and flexibility. The measurement results show that the absorption frequency can be shifted from 9.8 to 11.3 GHz, the peak absorption rate at each absorption frequency remains above 99.6%, and the reflection amplitude modulation can be achieved simultaneously at each absorption frequency. The proposed absorber integrates multiple modulation functions for electromagnetic waves, and the overall structure is optically transparent and flexible. Therefore, it can contribute to many practical wave absorbing applications.

Structural, Magnetic, and Electrical Investigations of PVA/Ni Ferrite/(MoS2)x Nanocomposites.

Transition metal sulfides (TMDs) possess exceptional dielectric properties and a narrow band gap, rendering them highly efficient as electromagnetic absorbing materials. Among these TMDs, the two-dimensional MoS2 nanosheet has received significant attention in research. However, the quest for new absorbers no longer finds satisfaction in solitary absorption mechanisms. This article introduces a successful method for creating PVA/NiFe2O4/(MoS2)x nanocomposites via a straightforward sol-gel technique, wherein porous amorphous NiFe2O4 microspheres are integrated into MoS2 nanosheets. The investigation uncovers that the incorporation of MoS2 results in an enhanced complex permittivity, facilitating the attainment of a desirable permittivity level. The PVA/NiFe2O4/(MoS2)x nanocomposite absorber exhibits an incredibly low reflection loss (RL) of -16.75 dB at a mere thickness of 1 mm, achieved through the cooperative interaction of dielectric and magnetic loss, along with the advantages of the structure and composition. Consequently, the PVA/NiFe2O4/(MoS2)x nanocomposites effectively absorb electromagnetic waves. Therefore, it is posited that MoS2-based composites hold great promise as highly effective microwave absorbers, boasting strong absorption intensity and a wide absorption frequency range, given the exceptional performance of the as-fabricated PVA/NiFe2O4/(MoS2)x nanocomposites.

Semi-self-similar fractal cellular structures with broadband sound absorption

Honeycomb core materials, recognized for their excellent sound absorption and load-bearing capabilities, are widely employed in engineering applications. The back cavity shape of honeycomb structure absorbers plays a crucial role in their sound absorption performance. In this study, the honeycomb structure absorbers are re-designed using fractal design principles, enabling a modification of the acoustic properties of traditional honeycomb-type absorbers and a significant enhancement in the sound absorption frequency band. The theoretical predictions of the semi-self-similar fractal honeycomb absorber structure are validated through finite element simulations and experimental studies, exhibiting remarkable consistency. The findings indicate that compared to single-layer first-order structures, the performance of dual-layer second-order fractal element Helmholtz resonators is significantly improved. Relative to conventional honeycomb panel structures, the fractal design approach markedly enhances the semi-absorption bandwidth of the absorbers, with an increase in the fractal order further broadening the sound absorption frequency band. The innovation of achieving broadband absorption through fractal resonators not only represents a new direction in the design of advanced honeycomb core materials but also holds substantial promise in the field of noise control.

Effect of Reduced Graphene Oxide on Microwave Absorbing Properties of Al1.5Co4Fe2Cr High-Entropy Alloys.

The microwave absorption performance of high-entropy alloys (HEAs) can be improved by reducing the reflection coefficient of electromagnetic waves and broadening the absorption frequency band. The present work prepared flaky irregular-shaped Al1.5Co4Fe2Cr and Al1.5Co4Fe2Cr@rGO alloy powders by mechanical alloying (MA) at different rotational speeds. It was found that the addition of trace amounts of reduced graphene oxide (rGO) had a favorable effect on the impedance matching, reflection loss (RL), and effective absorbing bandwidth (EAB) of the Al1.5Co4Fe2Cr@rGO HEA composite powders. The EAB of the alloy powders prepared at 300 rpm increased from 2.58 GHz to 4.62 GHz with the additive, and the RL increased by 2.56 dB. The results showed that the presence of rGO modified the complex dielectric constant of HEA powders, thereby enhancing their dielectric loss capability. Additionally, the presence of lamellar rGO intensified the interfacial reflections within the absorber, facilitating the dissipation of electromagnetic waves. The effect of the ball milling speed on the defect concentration of the alloy powders also affected its wave absorption performance. The samples prepared at 350 rpm had the best wave absorption performance, with an RL of -16.23 and -17.28 dB for a thickness of 1.6 mm and EAB of 5.77 GHz and 5.43 GHz, respectively.

Near-infrared H2S telemetry system under non-cooperative target with a novel mixed heterodyne optical structure scheme for high efficiency

A gas leakage telemetry system under non-cooperative target was designed and developed based on laser absorption spectroscopy technology, targeting the combination frequency absorption band of Hydrogen sulfide (H2S) gas molecules. A distributed feedback (DFB) laser centered at 1578 nm was adopt, with mature packaging process and high market maturity. The returned signal of diffuse reflection is extremely weak, decreasing exponentially with the increase of telemetry distance, and direct detection technology is difficult to achieve ideal performance at telemetry distance and lower detection limit. Thus, heterodyne detection technology was introduced to significantly amplify diffuse reflection signal and improve the signal-to-noise ratio (SNR) of telemetry system. For further detection sensitivity, wavelength modulation spectroscopy (WMS) technology was combined to suppress background noise through the electrical modulation of DFB laser. Alternating signal was applied to the laser to alter its output characteristics during the process of laser oscillation. Compared with exterior modulation methods, this interior modulation method does not require additional modulator, which avoids optical loss and is more economical. Combining the advantages of fiber structure and space optical path structure, a novel mixed heterodyne optical structure which was more applicable to this system was independently designed after the specific analysis of main noise sources. Then, the effect of heterodyne detection technology was verified in contrast of direct detection technology. Sensor performance was validated through calibration and stability experiments. The limit of detection (LoD) reached a minimum of 3.44 parts-per-million (ppm·m) with a 98 s averaging time. And the packaged system was fully capable of detecting the hazardous critical concentration of H2S and acting as an alarm mechanism.

Low-frequency broadband sound absorption of the metastructure with extended tube resonators and porous materials

A composite acoustic metastructure consisting of double porous materials and resonators with extended tubes is proposed to seek low-frequency broadband sound absorption, considering the low-frequency absorption of resonators and medium–high frequency absorption of porous materials. Based on the double porosity theory and finite element simulation, the sound absorption performance of the composite metastructure is investigated, and the numerical results are verified by experiments. It has been demonstrated that the metastructure with porous materials arranged vertically or horizontally can exhibit a sound absorption coefficient greater than 0.5 at 265–2000 Hz and greater than 0.8 at 760–2000 Hz, which is significantly superior to the existing sound absorption structure with resonator and porous material with the same thickness. The dependence of the sound absorption performance on the geometric parameters of the extended tubes and the porous materials is revealed. On the premise of keeping the cross-section shape of the extended tube and the arrangement of the porous material unchanged, sound absorption performance at low frequencies depends on the diameter, length, and porosity of the extended tubes, whereas sound absorption performance at medium–high frequencies is primarily determined by the percentage of porous materials. Finally, an improved multiple population genetic algorithm (IMPGA), improved by introducing a weight factor function, is used to optimize the parameters of the composite metastructure in a finite space with a thickness of 50 mm, and the sound absorption coefficient was greater than 0.5 in even lower and broader frequency range of [225,2000] Hz. Additionally, the IMPGA can be adjusted to achieve broadband sound absorption within the target frequency range. It provides a new exploration for acoustic material design for low-frequency broadband sound absorption.

Adjustable sound absorbing metastructures for low-frequency variable discrete sources

Low-frequency discrete variable noise sources, such as those in engines and fans, are frequently encountered in daily life. Due to the variability in noise frequency and the inherent characteristics of longer wavelengths, traditional acoustic structures face challenges in effectively absorbing such variable noise below 600 Hz. To address this, we propose using multiple-frequency adjustable sound absorption elements in parallel for variable low-frequency noise absorption. Each element's absorption frequency can be adjusted by modifying its bottom cavity volume. A theoretical model based on Helmholtz resonance is developed and validated through simulations and experiments, achieving high-efficiency sound absorption (α > 0.95) in the 260–520 Hz range. This model quantifies the dependence of absorption efficiency on design parameters and explores underlying mechanisms. For turbomachinery, a metastructure combines multiple elements with adjustable cavity volumes to broaden absorption bandwidth. Compared to non-adjustable materials, our metastructure achieves superior sound absorption below 600 Hz, broadening effective bandwidth by over 30 %. Limitations in extreme environments are discussed, suggesting potential improvements. This work can provide inspiration for the design of novel sound-absorbing structures with intelligent control of low-frequency variable noise and matching control systems.

In-depth investigations into symmetrical labyrinthine acoustic metamaterial with two micro-slit entries for low-frequency sound absorption.

Sound absorption below 1000 Hz has been extremely difficult through traditional barriers and absorbers, but it is required for noise control of appliances and machineries. Existing passive acoustic metamaterials attenuate low-frequency noise but with narrow bandwidths and bulky sizes. Hence, this paper proposes an acoustic metamaterial with enclosed symmetrical labyrinthine air channels and two micro-slits (configuration 1, identical slits; configuration 2, unequal length slits) at the end channels. Its theoretical model is established by acoustic impedance analysis using electro-acoustic analogy and validated numerically and experimentally. Sound absorption is found to happen as a result of impedance matching, Fabry-Perot-like labyrinthine resonances, and thermo-viscous losses in micro-slits. Parametric investigations reveal that increase in the number of channels, channel length, total height, and outer panel thickness shifts sound absorption peak to lower frequency but also decreases the magnitude and frequency range of absorption. Decreasing the channel width and slit width increases the sound absorption magnitude without changing absorption frequencies. Interestingly, unequal slit lengths perform better than equal slits by giving a lower frequency sound absorption with increased magnitude and frequency range, which is unlike that in existing labyrinthine metamaterials. Therefore, the proposed unequal slit metamaterial has enhanced low-frequency sound absorption and can be applied to appliances and machineries.

Perfect absorption frequency modulation, optical switching and slow-light multifunctional integrated device based on plasmon-induced absorption

Perfect absorption frequency modulation, optical switching and slow-light multifunctional integrated device based on plasmon-induced absorption

Thermal and acoustic characterization of nanofibrous polymeric structures for insulation applications

Nanofibrous structures are engineered materials for high-end applications. The impact of electrospinning settings on the thermal and acoustic properties of polyurethane (PU) nanofibrous structures is examined in this research. The excellent sound-absorbing properties of PU make it a versatile material that may be used in a variety of acoustic applications. The study focuses on how PU nanofiber morphology, such as fiber diameter and volume fraction, is affected by varying ambient conditions. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are used to examine the stability and thermal behavior of PU nanofibers. The findings show that raising the fiber volume fraction improves thermal stability and changes the way PU nanofibers behave thermally. PU nanofiber webs provide efficient sound absorption in low and intermediate frequency ranges according to the study's analysis of the sound absorption coefficients. According to the results, PU nanofiber webs may offer novel approaches to noise control, especially in situations where acoustic panel insulation is needed with no weight penalty.

Tunable asymmetric square split ring resonator based triple band metamaterial absorber for wireless communication system

This article presents a triple band square split ring with double circular split ring resonator incident angle-insensitive perfect metamaterial absorber. The MMA unit cell was manufactured using a FR4 substrate that had dimensions of 8 mm by 8 mm. With the flexibility of on-design adjusting of the highest absorption frequencies, the suggested MA displays peak absorption of 99.67 %, 99.85 %, and 99.97 % at 2.52 GHz, 6.99 GHz, and 9.28 GHz, correspondingly. The tuning metallic two circular split rings and square split ring resonator provide the possibility of frequency modification throughout three distinct frequency ranges: the first frequency range extends from 2.45 GHz to 2.53 GHz, the second frequency range extends from 6.91 GHz to 7 GHz, and the third frequency range extends from 8.85 GHz to 10.32 GHz. Furthermore, the suggested MA displays near-zero absorption at an oblique incidence angle of up to 45° for both the TE as well as TM modes. The unit cell demonstrates single negative properties, such as an effective medium ratio (EMR) of 14.88 and a quality factor (Q factor) that is more than 30 for both the TM mode as well as the TE mode. An equivalent circuit successfully demonstrated its performance capability, which indicated that it would create an MMA of good quality when using ADS software. A comparison between the measured results of the suggested MMA and the simulated one reveals that there is a significant amount of a similarity between both of them. Because of its easy design within small dimension, wide angular stability, strong absorption, good EMR, and flexibility to frequency tuning is suitable for a wide range of wireless communication system, especially satellite applications like electromagnetic interference reduction, radar systems, imaging, and stealth technology.

Bohr’s atomic model and the probabilistic reality

An analysis of applying the property of speed instantaneity to electronic transitions (i.e., transitions of the atomic electron that are not instantaneous), instead of quantum jumps (i.e., instantaneous transitions), during a complete oscillation for the process of Bohr’s model of the atom absorbing and emitting electromagnetic radiation (i.e., photon) reveals a discontinuity that is conserved as an emitted electromagnetic radiation (i.e., photon) discontinuity. The frequency of the oscillations of the atomic electron (i.e., electric charge) and induced magnetic field for the transitions of the atomic electron (i.e., electric charge) during the complete oscillation for the absorption and emission process (of Bohr’s atomic model) is conserved as the frequency of the oscillating electric and magnetic fields of the emitted electromagnetic radiation (i.e., photon). The conserved frequency and discontinuity (based on speed instantaneity and electronic transitions that are not instantaneous) of the atomic absorption and emission process (of Bohr’s atomic model) lead to predicting the need for Planck’s constant (i.e., quantum of action) without the use of probability. Planck claimed the interpretation of reality must change if his method of deriving the radiation law stood on a physical concept. Einstein, whom Planck credited as the first to make an advancement in the quantum field, unknowingly introduced a quantized two-dimensional discontinuum geometry that is one of the foundations on which a table of five realities used in physics was developed for making predictions. Using the table of realities, locality is redefined, and entanglement is demystified.

Design of dual-LSPR Bi/W18O49 composite and its red-light driven photocatalytic property in the photocatalytic degradation of PPCPs

Photocatalysis has become an increasingly popular method to treat pharmaceuticals and personal care products (PPCPs) in a water matrix due to its green and energy-saving nature. However, the development of high-efficiency catalysts to remove such refractory organic pollutants still faces many challenges. Herein, an urchin-like composite, Bi/W18O49, was designed and prepared via solvothermal process followed by magnetron sputtering method. The photocatalytic performance of Bi/W18O49 for PPCPs removal proved to be superior under red light (610 nm, 1.23E4 lm) compared with pure WO3 or W18O49, due to better light absorption property and frequency matching between the stronger plasmon resonance (dual-LSPR effect) and incident light irradiation. Thorough experiments were conducted to identify the unique properties of Bi/W18O49, and they demonstrated that the composite state contained plenty of oxygen vacancies and the dual-LSPR effect was vital to the efficient removal for pollutants, as the effect guarantees OV level, hot electron transfer, stable light response ability and more positive potential. The photocatalytic results show that the removal efficiency of trimethoprim, acetaminophen, and tetracycline by Bi/W18O49 could reach 93 %, 87 %, and 62 %, respectively. Combined with density functional theory (DFT) calculations and analysis, trapping tests, and LC-MS measurement, the degradation pathways of those pollutants were described in detail as well. Additionally, different influencing factors such as the concentration of catalyst and pollutants, pH of the solution, various inorganic and organic species were comprehensively investigated, and the reusability and stability property of the product performed well. To the best of our knowledge, this is the first time such Bi/W18O49 composite was prepared and applied in treating PPCPs, representing a new strategy for effective wastewater treatment via the construction of LSPR materials.

Design, Development and Evaluation of Tetracycline Controlled Release Microspheres

Microsphere drug delivery methods have been used to boost efficacy, reduce toxicity, and improve patient compliance. Additional benefits of using microspheres to deliver medications include controlled drug release, improved bioavailability, and targeted drug delivery to the desired location. In order to achieve the required therapeutic effect, hydroxypropyl methyl cellulose K4M and sodium alginate are used as a polymer in microsphere delivery system and different concentration of aluminium chloride is used as cross linking agent. The advantage of microsphere formulations over traditional tablet or capsule formulations is that they increase the surface area exposed to the absorption site, boosting medication absorption and reducing drug dose frequency. Tetracycline is a broad-spectrum antibiotic that is frequently used to treat illnesses like pneumonia and respiratory tract infections. The encapsulation effectiveness, particle size, in -vitro release analysis and release kinetics of the microsphere formulations was assessed.

Development of tunable acoustic materials with inline cavity structure for enhanced sound absorption and transmission loss

This article presents an innovative approach to design and characterize an acoustic material with tunable sound absorption and transmission properties. The material incorporates an inline cavity structure, created by extracting a sphere and a cylinder from a cubic unit cell, resulting in unique inlet and outlet ports. Four samples of varying thicknesses (in multiples of 5 mm) were prepared using 3D printing technology from UV-cured standard resin. Sound Absorption Coefficient (SAC) and Sound Transmission Loss (STL) were determined in the frequency range of 0.5–6.3 kHz using an Impedance Tube Apparatus. Peak SAC values gradually declined from 0.99 to 0.85 with sample thickness increasing from 5 to 20 mm. Likewise, the corresponding peak absorption frequencies of the test samples decreased from 4.95 to 1.95 kHz. The STL values varied between 4 dB to as high as 50 dB within the frequency range of 0.5–2 kHz. In addition, the STL values clearly showed a periodic pattern over the entire range of measurement, irrespective of the changes in thickness. Beyond 2 kHz, the periodic variation remained within a range of 18–38 dB for all the samples. Hence multiplying the unit cells along the transmission path had no remarkable effect on STL. Also, the impact of air gap thickness (10 mm, 20 mm, and 30 mm) on the acoustic properties of the samples was investigated. With the insertion of an air gap thickness of only 10 mm, the peak absorption frequency drastically shifted from 4.95 kHz to 1.275 kHz in the case of a 5 mm thick sample. Similar changes in the material's resonant behaviour with changing air gaps were visible for all other samples. The experimental results, summarily illustrate the role of thickness, internal structure, and air gap thickness in tailoring sound absorption and transmission capabilities. Hence the acoustic properties of the developed material are tunable which offers promising applications in soundproofing and noise reduction across both indoor and outdoor installations. In conclusion, this research demonstrates a novel approach to acoustic material design and its characterization, paving the way for optimized acoustic performance in engineering applications.

Electron irradiation modified point defects of SiC nanoparticles with tunable high electromagnetic wave absorption

Silicon carbide nanoparticles (SiC nps) were modified by changing the injection amount using 1 MeV high-energy electron as radiation source. When the injection volume reaches 5ⅹ1013 cm−2, the irradiated particles produce defect structures sufficient to optimize the electromagnetic wave absorption performance. With the increase of beam amount, the value of g detected by electron paramagnetic resonance (EPR) energy spectrum moves towards the silicon suspension bond, and the macroscopic electromagnetic wave absorption peak gradually moves towards the low frequency, accompanied by the enhancement of absorption intensity and the increase of absorption bandwidth. When the injection volume reaches 3ⅹ1014 cm−2, the loss value of −62.79 dB is achieved at the optimal thickness of 2.56 mm, and the absorption frequency band covers the entire Ku band. SiC presents point defects, and carbon atoms leave the original lattice position due to electron irradiation, forming carbon vacancies, resulting in uneven charge distribution inside the material, resulting in dipoles of orientation polarization, which further affects the electromagnetic wave absorption performance. As the irradiation dosage increases, the defects become denser and purer. This leads to higher electromagnetic wave absorption intensity and a correspondingly lower optimal absorption frequency. Thus, the modification of SiC nps through irradiation achieves tunable absorbers.

Azimuth Angle Dependence of Polarized Infrared Spectra of Injection-Molded Polyoxymethylene.

Injection-molded polyoxymethylene (POM) has molecular chains mainly oriented in the injection direction. We investigated the directional dependence of the polarized infrared reflection and attenuated total reflection spectra by rotating the anisotropic POM sample. Because of the strong absorption and large frequency dispersion of the C-O vibration in the main-chain direction, we found phenomena such as shoulder wing generation that resulted from the mixing of optical responses attributed to the vibration in the main chain and that in the direction perpendicular to the main chain. The spectra of the directional dependence can be explained qualitatively because of the anisotropy of the mode with large frequency dispersion.

Narrow-band and highly absorbing fano resonance in a cavity-coupled dielectric metasurface

Metamaterial resonance offers a flexibility in engineering the frequency and bandwidth of light absorption for a variety of optoelectronic applications such as wavelength-selective photodetection, optical sensing and infrared camouflaging etc. In this paper, we demonstrate a class of metal-dielectric thin-film cavity-coupled dielectric metasurfaces, which feature Fano resonances with both narrow bandwidth and strong light absorption. Our fabricated metasurface consists of a Si cuboid array on top of a SiO2 film backed with a metallic Cu layer. The weak coupling between electric mie mode in Si cuboid and Fabry–Perot mode within the SiO2 spacer layer yields a Fano resonance at 4.19 μm wavelength, which exhibits a strong light absorption of 65.8% and a quality (Q) factor of 112. The strongly absorbing Fano resonance is tunable within the 3–5 μm band by varying geometric parameters of the metasurface. To reveal potential application of the metasurface, the Fano resonance is applied in refractive index sensing and exhibits a sensitivity of 518.75 nm RIU−1 and a figure-of-merit (FoM) of 14.82 RIU−1. These results suggest that cavity-coupling presents an effective way in reducing the resonance bandwidth and enhancing light absorption in dielectric metamaterials, which holds promise for expanding the properties and device functionalities of metamaterials.